The present invention relates to a toner and a developer for developing electrostatic images used in image forming methods, such as electrophotography, electrostatic recording and magnetic recording, a process for production thereof, and an image forming method.
Hitherto, a large number of electrophotographic processes have been known, inclusive of those disclosed in U.S. Pat. Nos. 2,297,691; 3,666,363; and 4,071,361. In these processes, in general, an electrostatic latent image is formed on a photosensitive member comprising a photoconductive material by various means, then the latent image is developed with a toner, and the resultant toner image is, after being transferred onto a transfer material such as paper, as desired, fixed by heating, pressing, or heating and pressing, or with solvent vapor to obtain a copy. The residual toner on the photosensitive member without being transferred is cleaned as desired by various methods, and then the above steps are repeated.
Accordingly, it has been required to provide a toner excellent in releasability, lubricity, and transferability. For this reason, toners containing a silicone compound have been disclosed in Japanese Patent Publication (JP-B) 57-13868, Japanese Laid-Open Patent Application (JP-A) 54-48245, JP-A 59-197048, JP-A 2-3073, JP-A 3-63660, U.S. Pat. No. 4,517,272, etc. However, in such a toner containing a silicone compound directly added thereto, a silicone compound lacking mutual solubility with the binder resin shows a poor dispersibility and cannot be uniformly contained in individual toner particles, thus being liable to result in a fluctuation in chargeability of toner particles and a toner showing an inferior developing performance in a continuous use.
A corona discharger has been generally widely used in a printer or a copying machine utilizing electrophotography, as a means for uniformly charging the surface of a photosensitive member (electrostatic image-bearing member) or a means for transferring a toner image on a photosensitive member. On the other hand, a contact charging or transferring method of causing a contact charging member to contact or be pressed against a photosensitive member surface while externally applying a voltage has been developed and commercialized.
Such a contact charging method or a contact transfer method has been proposed in, e.g., JP-A 63-149669 and JP-A 2-123385. In such a method, an electroconductive elastic roller is abutted against an electrostatic image-bearing member and is supplied with a voltage to uniformly charge the electrostatic image-bearing member, which is then subjected to an exposure and a developing step to have a toner image thereon. Further, another electroconductive elastic roller supplied with a voltage is pressed against the electrostatic image-bearing member and a transfer material is passed therebetween to transfer the toner image on the electrostatic image-bearing member onto the transfer material, followed by a fixing step to obtain a copied image.
Accordingly, a greater importance is attached to the releasability, lubricity and transferability of a toner, and a uniformity among the toner particles is required also for this purpose. In order to solve the problem, a toner obtained through polymerization has been proposed in JP-A 57-11354, JP-A 63-192055, etc., but the toner is liable to cause an excessive slippage and by-passing of toner particles at the cleaning section. A similar problem is liable to be caused in capsule toners containing a silicone compound which have been also proposed in a large number.
Compared with a conventionally widely used transfer means utilizing a corona discharge, a contact transfer means can enlarge the area of attachment of a transfer material onto a latent image-bearing member by controlling the force of pressing the transfer roller against the latent image-bearing member. Further, the transfer material is positively pressed and supported against the transfer position, it is possible to minimize a synchronization failure by the transfer material-conveying means and the transfer deviation due to looping or curling of the transfer material. Further, it also becomes easy to comply with the requirement of a shorter transfer material conveying path and a smaller diameter of latent image-bearing member accompanying the size reduction of image forming apparatus.
On the other hand, in such an apparatus of performing a transfer by abutting, a certain pressure is necessarily applied to the transfer apparatus because a transfer current is supplied from the abutting position. When such an abutting pressure is applied, a pressure is also applied to the toner image on the latent image bearing member, thus being liable to cause agglomeration of the toner.
Further, in case where the latent image-bearing surface is composed of a resin, an attachment is liable to be caused between a toner agglomerate and the latent image-bearing member to hinder the transfer to the transfer material and, in an extreme case, a part of a toner image showing a strong attachment is liable to cause a transfer failure to result in a lack of toner image.
The above phenomenon is pronounced in development of line images of 0.1-2 mm. This is because edge development is predominant at line images to provide a large coverage with toner, which is thus liable to cause agglomeration under pressure and transfer failure resulting in a lack. A toner image formed in such instance provides a copied image having only a contour. This defective phenomenon is called xe2x80x9ctransfer dropout (resulting in a hollow image)xe2x80x9d.
Such a transfer dropout noticeably occurs on a thick paper of 100 g/cm2 or large, an OHP film having a high degree of smoothness and on a second face during a both face copying. In the case of a thick paper and an OHP film, such a transfer dropout might be frequently caused because of a shortage of transfer electric field and a strong pressure because of a thick transfer material.
The transfer dropout might be frequently caused on a second face in the both face copying because the second face is also passed through a fixing device in the first face-copying so that the adhesion of a toner onto the second face is hindered.
For the above reasons, a transfer apparatus imposes serious requirements on a transfer material while it provides many advantages, such as size reduction and economization of electric power consumption.
On the other hand, a method of improving the dispersibility of a silicone compound by causing inorganic fine powder to adsorb the silicone compound and adding the inorganic fine powder into toner particles has been disclosed in JP-A 49-42354, JP-B 58-27503 and JP-A 2-3073. However, a toner and developer having further improved releasability and transferability are desired.
Addition of particles treated with a silicone compound into toner particles has been disclosed in JP-A 59-200251, JP-A 58-80650, JP-A 61-279865, JP-A 1-100561, JP-A 1-105958, JP-A 2-126265, JP-A 2-287367, JP-A 3-43748, JP-A 4-274445, and JP-A 3-53260. In these references, the silicone compound is caused to adhere onto the particle surfaces for hydrophobization, increased dispersibility of particles and increased charge, so that the silicone compound does not move to the toner particle surfaces. Accordingly, a toner and a developer having further improved releasability, lubricity and transferability are still desired.
Developers including toner particles to the surface of which silicone oil, etc., has been attached, have been disclosed in JP-B 44-32470, JP-B48-24904 and JP-B 52-30855. These developers are accompanied with difficulties such that a small amount of silicone oil, etc., fails to uniformly attach to and cover the toner particles or is liable to be transferred from the toner particles to another member to be lost from the toner particle surfaces. As a result, the effect thereof cannot last for a long period or becomes ununiform, thus resulting in a charging irregularity and an adverse effect to the developing performance. Further, it is difficult to attach the silicone oil, etc. to form and retain a thin and uniform layer of the silicone oil on the toner particle surfaces, so that the effect thereof does not last for a long period but result in a poor developing performance.
Further, in the case of using a developer comprising a mixture of toner particles comprising a binder resin and a colorant, such as a magnetic material, and a flowability improver, such as silica, in an image forming apparatus including a contact charging means and a contact transfer means, there is liable to cause difficulties such that a slight amount of residual toner on the photosensitive member not removed in the cleaning step after the transfer step sticks to the charging roller and the transfer roller pressed against the photosensitive member, and the sticking and amount of such toner are enhanced or increased on an increased number of copying operations to result in a toner melt-sticking and cause charging failure, cleaning failure or transfer failure. As a result, the resultant images are liable to be accompanied with difficulties, such as a decrease and irregularity of image density, white spots in a solid black image, and black spots in a solid white image.
In order to remove a residual toner on a photosensitive member after a transfer step, various means, such as those according to the blade scheme, fur brush scheme and magnetic brush scheme, have been known, but it is difficult to completely remove the residual toner on the photosensitive member after the transfer step.
In order to obviate such a toner sticking onto a photosensitive member, it has been proposed to add both a friction-reducing substance and an abrasive substance to a toner in JP-A 48-47345. However, the friction-reducing substance is liable to form an adhering filmy substance so that the toner is liable to form a film of the friction-reducing substance on a charging roller and a transfer roller to cause charging failure and transfer failure, when used in an image forming apparatus equipped with contact charging means and contact transfer means.
In a medium-speed copying machine, an organic photosensitive member (organic photoconductor) is generally used for the purpose of size-reduction and cost-reduction. In order to reduce the friction of the surface layer of particularly an organic photosensitive member to prevent the deterioration of a charging characteristic, it has been proposed to use an organic photosensitive member containing in its surface layer a lubricant, such as a fluorine-containing resin fine powder, in JP-A 63-30850. Such an organic photosensitive member containing the lubricant is actually provided with a prolonged life, but is caused to have a lower surface smoothness of the photosensitive member because the lubricant shows a poor dispersibility in a binder resin, such as polycarbonate resin, constituting the surface layer. As a result, if the photosensitive member is incorporated in an image forming apparatus including a contact charging means and a contact transfer means, the toner after development is liable to enter the surface concavity, and the performance of cleaning the residual toner is liable to be lowered to result in a toner sticking on the charging roller, the transfer roller and the photosensitive member.
An object of the present invention is to provide a toner and a developer for developing electrostatic images, a process for production thereof and an image forming method having solved the above-mentioned problems.
A more specific object of the present invention is to provide a toner and a developer for developing electrostatic images excellent in continual releasability, lubricity and transferability and free from deterioration with time and continuous image formation, a process for production thereof and an image forming method.
Another object of the present invention is to provide a toner and a developer for developing electrostatic images excellent in releasability, lubricity and transferability, and also in developing performance and durability, a process for production thereof and an image forming method.
Another object of the present invention is to provide an image forming method wherein a latent image-bearing member is used together with a member pressed thereagainst while suppressing the occurrence of damages, toner sticking and filming.
Another object of the present invention is to provide a toner and a developer for developing electrostatic images free from soiling a member to be pressed against a latent image-bearing member, thus being free from charging abnormality or transfer failure leading to image defects, a process for production thereof and an image forming method.
Another object of the present invention is to provide a toner and a developer for developing electrostatic images excellent in cleanability and not causing by-passing of a cleaner or cleaning failure, a process for production thereof and an image forming method.
Another object of the present invention is to provide a toner and a developer for developing electrostatic images free from or capable of suppressing transfer dropout even on a diversity of transfer materials, a process for production thereof, and an image forming method.
A further object of the present invention is to provide a toner and a developer for developing electrostatic images capable of providing high-quality transfer images and fixed images faithful to a latent image, a process for production thereof and an image forming method.
A still further object of the present invention is to provide a toner and a developer for developing electrostatic images showing an improved cleanability even when attached onto a contact charging member and a contact transfer means, a process for production thereof and a image forming method.
According to the present invention, there is provided a toner for developing an electrostatic image, comprising toner particles; wherein each toner article comprises:
(i) 100 wt. parts of a binder resin having a glass transition point (Tg) of 50-70xc2x0 C.,
(ii) 0.2-20 wt. parts of solid wax, and
(iii) colorant particles carrying a liquid lubricant, magnetic powder carrying a liquid lubricant, or a mixture thereof;
the toner particle retaining the liquid lubricant at its surface.
According to another aspect of the present invention, there is provided a developer for developing an electrostatic image, comprising toner particles and an external additive; wherein each toner particle comprises:
(i) 100 wt. parts of a binder resin having a glass transition point (Tg) of 50-70xc2x0 C.,
(ii) 0.2-20 wt. parts of solid wax, and
(iii) particles carrying a liquid lubricant;
the toner particle retaining the liquid lubricant at its surface;
said external additive comprising inorganic fine powder treated with an organic agent.
According to a further aspect of the present invention, there is provided a process for producing a developer, comprising:
blending a binder resin, a solid wax and particles carrying a liquid lubricant to obtain a blend,
melt-kneading the blend to obtain a melt-kneaded product,
cooling the melt-kneaded product,
pulverizing the resultant cooled melt-kneaded product to obtain a pulverized product,
classifying the pulverized product to form toner particles, and
blending the toner particles with inorganic fine powder treated with an organic agent.
According to a still further aspect of the present invention, there is provided an image forming method, comprising:
charging an electrostatic image-bearing member by a charging means;
exposing to light the charged electrostatic image-bearing to form an electrostatic image thereon;
developing the electrostatic image with a developer to form a toner image on the electrostatic image-bearing member, said developer comprising a mixture of toner particles and inorganic fine powder treated with an organic agent; and
transferring the toner image on the electrostatic image-bearing member to an intermediate transfer member or a transfer material;
wherein each of said toner particles comprises:
(i) 100 wt. parts of a binder resin having a glass transition point (Tg) of 50-70xc2x0 C.,
(ii) 0.2-20 wt. parts of solid wax, and
(iii) colorant particles carrying a liquid lubricant, magnetic powder carrying a liquid lubricant, or a mixture thereof,
the toner particle retaining the liquid lubricant at its surface; and
at least one of said charging means transfer means is contactable with said electrostatic image-bearing member.